The present invention relates generally to a photoelectric angle measuring arrangement and more particularly to a photoelectric measuring arrangement of the type which includes a circular graduation.
Angle measuring arrangements of the interferometric type which include a graduation carrier carrying a circular graduation, and a scanning arrangement which scans the diameter of the circular graduation are typically used in processing machines which measured the relative position of a tool with respect to a workpiece which is to be processed.
For example, in the dissertation "Photoelektrische Messung der Anderung von Langen-Order Winkelpositianen mit Hilfe von Beugungsgittern" (Photoelectric Measurements of the Change of Length or Angular Positions With the Aid of Refraction Grids) F. Hock, 1975 illustrates (in FIG. (86) an angle measuring arrangement for the elimination of the eccentricity error of the angle graduation of a graduating disk. In this disclosed arrangement, a light beam from a light source penetrates a first angle graduation zone of the angle graduation of the graduating disk through a condenser. The light beam is split into two partial beams by feeding the light beam through a first pentaprism, a first deflecting prism and a first lens to a Wollaston prism. The two partial beams penetrate a second angle graduation zone on the graduating disk, which lies diametrally opposite to the first angle graduation zone, through a second lens, a second pentaprism and a second deflecting prism. The two partial beams then are received on two photoreceivers over a polarizing divider prism. This angle measuring arrangement has the disadvantage that it has large dimensions and requires a large expenditure in assembling and adjusting due to the multiplicity of optical elements.
The publication "Motion" July/August 1986 in an article entitled "Laser Rotary Encoder" by Nishimura et al. also discloses (on pages 3 and 4) an angle measuring arrangement for the elimination of the eccentricity error of the angle graduation of a graduating disk. In this disclosed arrangement, a light beam from a laser diode is split into two partial beams by a polarizing divider prism. A first partial beam penetrates a first angle graduation zone of the angle graduation of the graduating disk over a first phase plate and a flat mirror to generate refraction beams. The positive first order refraction beam is then reflected back into the polarizing divider prism by means of a first reflector through the first angle graduation zone, the first mirror and the first phase plate. The reflected positive refraction beam is received by a first photoreceiver over a third phase plate, a beam divider and a first polarization plate. The second partial beam penetrates a second angle graduation zone of the angle graduation of the graduating disk over a second phase plate and a second mirror to generate refraction beams. The negative first order refraction is reflected back into the polarizing divider prism by means of a second reflector through the second angle graduation, the second mirror and the second phase plate. The reflected negative refraction beam is received by a second photoreceiver over the third phase plate, the beam divider and over a second polarization plate. This angle measuring arrangement is relatively expensive and requires a large expenditure in assembling and adjusting.
German DE-A1-36 33 574 describes a simpler, and thus more economically produced, angle measuring arrangement having smaller dimensions. The angle measuring arrangement disclosed in this reference is insensitive to wobble errors of the graduation carrier. Eccentricity errors are also eliminated.
It is desirable to provide a high-resolution angle measuring arrangements with even smaller construction size and an even simpler construction than available systems which also provides a measuring accuracy and operating reliability surpassing those of conventional angle measuring arrangements.
Therefore, in view of the above it is an object of the present invention to provide a high-resolution angle measuring arrangement which may be constructed with small construction size.
It is a further object of the present invention to provide a high resolution angle measuring arrangement with a simple construction.
It is still a further object of the present invention to provide a high resolution angle measuring arrangement which provides a higher accuracy and operating reliability than presently available angle measuring arrangements.